7-Chloro-4-[(7-chloroquinolin-4-yl)sulfanyl]quinoline dihydrate

In the title thioether dihydrate, C18H10Cl2N2S·2H2O, the S-bound quinolinyl residues are almost orthogonal, forming a dihedral angle of 72.36 (4)°. In the crystal, the four water molecules are connected via an eight-membered {⋯OH}4 synthon with each of the four pendent water H atoms hydrogen bonded to a pyridine N atom to stabilize a three-dimensional architecture.

In the title thioether dihydrate, C 18 H 10 Cl 2 N 2 SÁ2H 2 O, the Sbound quinolinyl residues are almost orthogonal, forming a dihedral angle of 72.36 (4) . In the crystal, the four water molecules are connected via an eight-membered {Á Á ÁOH} 4 synthon with each of the four pendent water H atoms hydrogen bonded to a pyridine N atom to stabilize a threedimensional architecture.
The water molecules play a pivotal role in stabilizing the crystal structure, forming hydrogen bonds to each other and to the quinolinyl-N atoms, Table 1. The water···water interactions each to eight-membered {···OH} 4 synthons with each pendent water-H atom hydrogen bonded to a quinolinyl-N atom to stabilize a three-dimensional architecture, Fig. 2.

Experimental
A modification of a published procedure was adopted (Natarajan et al., 2008). A solution of 4,7-dichloroquinoline (0.5 g) in EtOH (20 ml) was heated to 323 K. Thiourea (0.20 g.) was added and the mixture was stirred for 5 min. and then cooled to room temperature. The white solid was filtered off and was extracted into 0.2 M NaOH solution. The precipitate, bis(7-chloroquinolin-4-yl)sulfide, was collected and recrystallized from EtOH as the dihydrate; M.pt. 436-439 K;lit. M.pt: 439-440 K (Surrey, 1948).

Refinement
The C-bound H atoms were geometrically placed (C-H = 0.95 Å) and refined as riding with U iso (H) = 1.2U eq (C). The O -H atoms were located in a difference Fourier map, and were refined with a distance restraint of O-H = 0.84±0.01 Å and with H···H = 1.39±0.03 Å; their U iso values were constrained to 1.5U eq (O).  The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.

Figure 2
A view in projection down the a of the unit-cell contents of (I). The O-H···O and O-H···N hydrogen bonds are shown as orange and blue dashed lines, respectively. Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.